Work machines, for example, hydraulic excavators, often perform tasks using a work tool. For example, a hydraulic excavator may dig a trench in the earth using a work tool, such as a bucket. An operator typically controls the machine and work tool. In the case of an excavator, an operator controls the excavator's engine speed, forward movement, rotational movement, the movement of the boom and the pitch and angle of the bucket. Controlling all aspects of the excavator's movement requires a highly trained operator.
As an example operation, an excavator may be clearing a ditch. The operator orients the excavator to travel parallel to the ditch. The excavator may be positioned at any point along the ditch. The ground along the ditch may be uneven. For example, the ground at one point may slope towards the ditch and at another point the ground may slope away from the ditch. Thus, the excavator may be tipped along its roll axis. The operator guides the bucket along the ditch surface until the bucket fills with dirt. The operator then levels the bucket to maintain the captured load. As the operator raises the bucket out of the ditch, the boom is swung away from the ditch to dump the load. During the swing operation the bucket angle relative to the horizon changes by the amount the machine is tipped along its roll axis. Therefore, the operator must make constant adjustments to the level of the bucket to prevent spilling the load. Controlling all aspects of a work machine, such as an excavator, requires a highly skilled operator.
Even a highly skilled operator can not perform a ditch clearing operation as quickly when the excavator is tipped. After the operator fills and raises the bucket, the bucket is swung away from the ditch. However, the operator must constantly make adjustments to the angle of the bucket. In order to prevent the load from spilling, the operator often must slow the swing rate of the machine, so that the bucket angle adjustments can be made before any material spills from the bucket.
In addition to maintaining the work tool angle as the machine swings the bucket away from the ditch, the operator must vary the angle of the bucket during other steps in the machine's work cycle. For example, as the bucket approaches the dump point, the operator must vary the angle of the bucket such that the material in the bucket falls from the bucket and lands at the correct dump point. As the operator swings the machine back to the ditch, the angle of the bucket must be set at the correct angle to perform the next dig operation in the ditch. The correct dig angle may change based on the type and density of material being dug and the angle of the ditch with respect to both the surface of the earth and gravity.
Simple control schemes have been implemented to maintain a set work tool angle with respect to the earth. One exemplary system for maintaining a work tool angle is disclosed in U.S. Pat. No. 7,222,444 to Hendron et al. The disclosed system includes a tilt sensor attached to a bucket. The tilt sensor can sense bucket tilt angle relative to the earth and generate a corresponding bucket angle signal. A controller receives the bucket angle signal and generates a bucket control signal. Based on the bucket control signal, the machine moves the bucket to achieve the preselected angle with respect to the earth. While this system can maintain an approximately set angle for a work tool, it can not vary the angle of the work tool based on the task the machine is performing.
The foregoing background discussion is intended solely to aid the reader. It is not intended to limit the disclosure, and thus should not be taken to indicate that any particular element of a prior system is unsuitable for use within the disclosure, nor is it intended to indicate that any element is essential in implementing the innovations described herein. The implementations and application of the innovations described herein are defined by the appended claims.